Active Pd intermediates of the Suzuki-Miyaura reaction with low reactive aryl chlorides under “ligand-free” conditions

Abstract

Despite extensive studies regarding Pd intermediates reacting in the transmetalation step of the Suzuki–Miyaura reaction (SMR), direct evidence obtained under real turnover conditions supporting the widely accepted assumptions regarding the activity of Pd hydroxo complexes is lacking. Herein, results concerning the major reactivity of Pd-OH- and/or Pd-OR-containing complexes (RO− is the base anion) in the transmetalation step with arylboronic acid under “ligand-free” turnover conditions are presented. By contrast, aryl chloride activation was mainly realized through halide-containing Pd complexes. Data regarding the catalytic involvement of particular Pd species were obtained under real catalytic conditions by measuring differential selectivity of the competing reactions. In the reaction with demanding aryl chlorides catalyzed by “ligand-free” catalytic systems that is optimal from the viewpoints of environment, cost, and availability, the composition of active Pd complexes in the transmetalation step was similar to that for the reaction using more reactive aryl bromides and iodides.